DeFazio is the panel’s second-most-senior Democrat, and perhaps his biggest selling point — next to his legislative record — is his seniority.

It’s something many of DeFazio’s peers are particularly deferential about, and it has led to a large number of lawmakers flocking to his side of the field.

Last month, 20 self-identified progressive members of the House Democratic Caucus signed a letter supporting him.

“Peter has the seniority, the experience, the expertise, and the tenacity to challenge the Republicans’ ideological rhetoric,” they wrote. “He has ably served on the committee for 26 years — serving on every subcommittee — and mastered the wide range of natural resources issues confronting the committee.”

While DeFazio may be scoring inside endorsements, Grijalva is trying to rack up outside backing to help his bid.

Though many of the mainstream national environmental groups haven’t yet weighed in on the campaign, some organizations see the significance of elevating the Congressional Progressive Caucus co-chairman to a higher seat at the Democratic leadership’s table. And they are starting to speak up.

Mark Magaña, executive director of the National Latino Coalition on Climate Change, told CQ Roll Call that his organization is considering sending a support letter for Grijalva signed by its member organizations.

While Grijalva’s environmental record is integral to the coalition’s support, Magaña said, the congressman’s ascent to the ranking member slot would mean there would be another pro-immigration Democrat on the committee leadership roster.

“We need to increase that number, and this would be an important opportunity to do that,” he said.

To be sure, Magaña said his group couldn’t support Grijalva’s candidacy if he didn’t have an “exemplary” voting record on pollution and conservation issues. But it’s also important for Democratic leaders to consider where candidates stand on issues important to the Hispanic community, he said. DeFazio’s past votes on immigration — particularly his vote for the 2005 immigration overhaul backed by President George W. Bush that never became law — are worrisome, he said.

“We want to make sure that people who took that vote in a negative way are held accountable,” Magaña said.